1. Field of the Invention
The present invention relates to a machine tool equipped with an automatic tool changing device, and more particularly to such automatic tool changing device which is simple in construction.
2. Discussion of the Related Art
There is known a universal or multi-function machine tool or machining center capable of performing a variety of machining operations on workpieces and equipped with an automatic tool changing device which includes a tool magazine or tool storage drum accommodating a relatively large number of cutting tools, of either rotary type such as taps, drills, milling cutters (e.g., end milling cutters) and boring tools or non-rotary type such as lathe tools. The automatic tool changing device is adapted to return a used tool to the tool magazine, and select a new tool from the tool magazine and mount the selected new tool on a spindle of the machine, for example. Examples of machine tools equipped with such automatic tool changing device are disclosed in JP-A-63-267136 and JP-A-2-274448 (laid-open publications of unexamined Japanese Patent Applications).
The automatic tool changing device disclosed in JP-A-63-267136 utilizes vertical reciprocating movements of a spindle head to activate two cam mechanisms for exchanging tools at the tool mounting end of the machine spindle. Described more specifically, one of the cam mechanisms is used to control operations of a tool clamping mechanism for unclamping a used tool from the spindle and clamping a new tool to the spindle, and the other cam mechanism is used to control operations of a rotary tool changer arm for exchanging the tools. A crank lever provided on the spindle head is pivoted by a cam during upward and downward movements of the spindle head, and pivotal movements of the crank lever are converted into movements of the tool clamping mechanism to unclamp and clamp the tools. The rotary tool changer arm is rotatably disposed on the tool magazine, which is indexable to select a desired tool. The tool changer arm is spring-biased toward the spindle head, and the vertical movements of the spindle head cause a cam to rotate the tool changer arm for removing the used tool from the spindle and installing the new tool on the spindle.
In the automatic tool changing device disclosed in JP-A-2-274448, the spindle is moved to a predetermined tool change position at which the used and new tools are exchanged, and then returned to a machining position. The tool clamped on the spindle located at the tool change position is first gripped by one of a plurality tool grippers provided on an indexable tool magazine. Then, the tool is unclamped from the spindle by a hydraulic cylinder, and the tool magazine is advanced to remove the used tool from the spindle, rotated for indexing to bring the new tool into alignment with the spindle, and finally retracted to install the new tool on the spindle. The installed new tool is clamped by activation of the hydraulic cylinder, and the spindle is moved from the tool change position to the machining position.
Although the automatic tool changing devices described above are adapted to handle rotary cutting tools, similar mechanisms for exchanging the tools as described above are applicable to non-rotary cutting tools.
However, the automatic tool changing device disclosed in JP-A-63-267136 which uses a cam mechanism to control the tool clamping mechanism also uses another cam mechanism to control the rotary tool changer arm for exchanging the tools and is accordingly complicated in construction. On the other hand, the automatic tool changing device disclosed in JP-A-2-274448 requires an exclusive power source to activate the hydraulic cylinder for operating the tool clamping mechanism, and a detecting device for controlling the operation of the hydraulic cylinder. The use of such exclusive power source and detecting device leads to increased complexity of the tool changing device. Thus, the known automatic tool changing devices described above suffer from a relatively high cost of manufacture, and a relatively low degree of operating reliability, due to the constructional complexity.